A configuration of a normal main apparatus system is illustrated in FIG. 1. Referring to FIG. 1, the normal main apparatus system includes a plurality of main apparatuses 901-1, 901-2, . . . and 901-N. Here, all of main apparatuses 901-1, 901-2, . . . and 901-N comply with the same standard, and are assumed to comply with a second-standard. Therefore, the main apparatuses 901-1, 901-2, . . . and 901-N are referred to as second-standard main apparatuses 901-1, 901-2, . . . and 901-N. Each of the plurality of second-standard main apparatuses can function independently. In that case, all operations of the second-standard main apparatus 901 are controlled by a controller 903 included therein. By combining a plurality of the second-standard main apparatuses, it is possible to build out a main apparatus system. In this case, as illustrated in FIG. 1, the plurality of second-standard main apparatuses 901-1, 901-2, . . . and 901-N are connected to each other by cables 905. Further, only a controller 903-1 in one main apparatus 901 (a first second-standard main apparatus 901-1 in an example of FIG. 1) is validated and other controllers (a controller 903-2 of a second second-standard controller 901-2 to a controller 903-N of a Nth second-standard controller 901-N) of other main apparatuses 901 are invalidated. Further, the first second-standard main apparatus 901-1 to the Nth second-standard main apparatus 901-N are controlled by the controller 903-1 included in the first second-standard main apparatus 901-1.
FIG. 2 is a conceptual diagram which illustrates an inner structure and so forth of the second-standard main apparatus 901-s (s=1, 2, . . . , N). Referring to FIG. 2, the second-standard main apparatus 901-s includes a controller 903-s, a first base station interface 907-s-1 to a Mth base station interface 907-s-M, an empty slot 909-s and a backboard 911-s. The backboard 911-s is used for connecting the controller 903-s, the first base station interface 907-s-1 to the Mth base station interface 907-s-M and the empty slot 909-s mutually. The controller 903-s and the first base station interface 907-s-1 to the Mth base station interface 907-s-M have forms of card base plates inserted into slots of the backboard 911-s. A slot into which the card base plate is not inserted is the empty slot 909-s. 
The first base station interface 907-s-1 to the Mth base station interface 907-s-M are connected to a first base station 913-s-1 to a Mth base station 913-s-M respectively.
A first terminal 921-1 to a Lth terminal 921-L perform radio communication with any base station among the first base station 913-s-1 to the Mth base station 913-s-M according to a predetermined communication standard. The predetermined standard is, for example, PHS (Personal Handy-phone System), Wireless LAN (Local Area Network) standard, W-CDMA (Wideband-Code Division Multiple Access), or MIMO (Multiple Input Multiple Output).
On the basis of above configuration, in the main apparatus system, one terminal 921 connected to any base station 913-s-m (m=1, 2, . . . , M) connected to any second-standard main apparatus 901-s (s=1, 2, . . . , N) can communicate not only with another terminal 921 connected to any base station 913-s-m′ (m′=1, 2, . . . , M) connected to the main apparatus 901-s but also with the other terminal 921 connected to any base station 913-s′-m′ (m′=1, 2, . . . , M) connected to any other main apparatus 901-s′ (s′=1, 2, . . . , N). Therefore, the backboard 911-s relays data sent and received between the terminal 921 connected to any base station 913 included in the main apparatus system and the terminal 921′ connected to any base station 913′ included in the main apparatus system. This relay is performed by multiplexing the data with other data between other terminals and further demultiplexing them.
PTL 1 discloses an art that a switching equipment is connected to a computer which functions as a server device wherein the switching equipment does not include a time switch function and a switching control function which are included in a normal switching equipment, and a time switcher and a CPU included in the server device act for the time switch function and the switching control function.